In-container sterilization has many benefits over other forms of food and drink processing. It is usually continuous compared with batch based retort systems, can process very large volumes of identical product, does not require the product package to be sterile before filling or processing unlike aseptic processing systems and can process solids, liquids and component mixtures with minimal change to processing conditions.
That being said, it does have a number of drawbacks. Because of the relatively long dwell times, it does tend to over-process many products. It cannot compensate its processing conditions quickly to accommodate changes in product properties such as variations in incoming temperature and/or fluctuations in composition. Neither can it easily process different product without a significant time and production delay as system process conditions are modified. (Although many of these issues have subsequently been successfully resolved using the inventions taught in U.S. Patent Application 61/488,220, Newman).
However, by far the greatest limitation is the constraint the system's extreme operating conditions place on the types of product packaging that can be accommodated. With operating temperatures often exceeding 120° C. and operating pressures in excess of 2 atmospheres, packaging materials are usually limited to those able to withstand such extremes of processing conditions such as sealed metal cans and, to a somewhat lesser degree, glass jars and bottles. Such processing conditions generating high temperatures and pressure within the product container, the container is often exposed to over-pressurization, i.e. pressure is applied to the external surfaces to counter-act the increased pressure within the container and the stresses to the container structure and integrity.
In addition, the liquid/gaseous nature of the sterilizing media prevents the use of many newer packaging materials, particularly those made from laminated card or paperboard. The prolonged immersion times in a liquid and/or high humidity atmosphere will cause such materials to become water sodden and lose their physical strength and integrity.
Similarly, many of today's alternative packaging materials are polymer-based. These will delaminate, soften or melt under such extreme processing conditions, while the often significant expansion of the package contents, particularly the gas/air in the package headspace will lead to seam rupture, wall weakening and/or package burst.
Finally, many laminate-based packaging will, when subjected to high temperatures and/or high moisture content environments, cause breakdown products, many often toxic such as terephthalates and bis-phenol-A, to be released into the food product within. The same also occurs with metal can coatings in contact with high acid foods at elevated temperatures.
There have been many attempts to overcome some of these issues. Such innovation teaches the use of pressure release valves within the packaging (Hoffman, U.S. patent application Ser. No. 12/005,596), the use of non-toxic coatings on the inner walls of cans (McVay, U.S. Pat. No. 7,475,786), alternative package liner materials that do not release toxic by-products (Owens, U.S. Pat. No. 4,476,263) and polymers which can withstand higher processing temperatures without failure (Yamazaki, U.S. Pat. No. 4,206,299, Lohwasser, U.S. Pat. No. 7,008,501). However, none of these alone or in combination will resolve many of the practical limitations associated with utilizing modem packaging materials within the continuous, in-container, thermal processing environment.
As well as the processing environment constraints, there are several other packaging-related issues that also need addressing.
Because of the physical extremes encountered with in-container sterilization, the container has traditionally been of robust construction, e.g. steel cans or thick-walled glass jars and bottles. While this allows product to be sterilized to required time-temperature and pressure conditions, it does so at a cost in fact several costs.
Firstly, the thickness of the container adds weight and cost through space (it is usually not collapsible and occupies its full volume even when empty), storage (same reason) and transport.
Secondly, the wall thickness requires additional energy to both heat up and cool down while negatively effecting the rate of heat transfer between the energy source (water or steam) and the product inside. This in turn affects the resultant product quality.
Many aseptic packages display enhanced graphics which makes them more attractive than a label from a sales and marketing perspective. However, these are costly to produce but they cannot withstand the rigors of the in-container sterilization. Alternative graphics printed on heat shrinkable film have been developed for adding to retort packages and could be added to in-container sterilized products but again at additional cost and more production time.
The final issue applies to all packages whether aseptic, retort or continuous—and that is their protective function. All packaging has to be suitable for purpose, i.e. it must retain and preserve the contents under the conditions of storage and display. Steel cans and glass jars and bottles, by their very nature, tend to be moisture impervious and oxygen impervious. The property of being light impervious is either inherent or generated by the addition of dyes into the glass or the use of further packaging such as cartons and boxes.
The same physical properties are generated within flexible cartons, pouches and packs through multi-lamination where each layer of the laminate generates a specific property. For example, an aluminum layer makes the package air and light controlled, an EvOH layer protects the aluminum layer for attack from high acid foods, a polypropylene layer allows the aluminum layer to be heat sealed, etc. There are also usually water proofing layers on inner and outer surfaces and a graphics protective layer. The result is a very efficient but expensive packaging system.
Finally there is the issue of packaging sterilization. All aseptic packages have to be separately chemically and/or physically sterilized as the package itself cannot be exposed to the same conditions as their contents. Many retort packages are processed at temperatures and pressures that only minimally pasteurize the container.
The embodiments and preferred embodiments of this invention address all of these issues by adapting the manner in which packaging materials are used to contain the foodstuff, optimize its processing, increase its flexibility and yet substantially reduce processing time and costs.